Display guarding techniques

ABSTRACT

Embodiments described herein mitigate the effect of a coupling capacitance between a sensor electrode in a touch sensor and a display electrode in a display screen. An input device, which includes the touch sensor and display screen, may transmit a guarding signal on the display electrodes when performing capacitive sensing. In one embodiment, the guarding signal may have similar characteristics as a modulated signal (e.g., similar amplitude and/or phase) driven on the sensor electrode to detect interaction between the input device and an input object. By driving a guarding signal that is similar to the modulated signal onto the display electrodes, the voltage difference between the sensor electrode and display electrode remains the same. Accordingly, the coupling capacitance between the sensor electrode and the display electrode does not affect a capacitance measurement used to detect the user interaction.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.14/067,792, filed Oct. 30, 2013, entitled “DISPLAY GUARDING TECHNIQUES”which claims benefit of U.S. Provisional Patent Application Ser. No.61/885,473, filed Oct. 1, 2013 entitled “DISPLAY GUARDING TECHNIQUES”which are each herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention generally relate to managingparasitic capacitance when performing capacitive sensing, and morespecifically, to transmitting a guarding signal on display electrodesfor managing parasitic capacitance.

2. Description of the Related Art

Input devices including proximity sensor devices (also commonly calledtouchpads or touch sensor devices) are widely used in a variety ofelectronic systems. A proximity sensor device typically includes asensing region, often demarked by a surface, in which the proximitysensor device determines the presence, location and/or motion of one ormore input objects. Proximity sensor devices may be used to provideinterfaces for the electronic system. For example, proximity sensordevices are often used as input devices for larger computing systems(such as opaque touchpads integrated in, or peripheral to, notebook ordesktop computers). Proximity sensor devices are also often used insmaller computing systems (such as touch screens integrated in cellularphones).

SUMMARY OF THE INVENTION

One embodiment described herein is an input device that includes aplurality of sensor electrodes that establish a sensing region of theinput device and at least one display electrode configured to, duringdisplay updating, set a voltage associated with a pixel of a displaydevice. The input device further includes processing system coupled tothe plurality of sensor electrodes and the at least one displayelectrode to drive a modulated signal onto a first sensor electrode ofthe plurality of sensor electrodes to acquire a change in capacitivecoupling between an input object and the first sensor electrode during afirst period and operate the at least one display electrode in a guardmode to mitigate an effect of a coupling capacitance between the firstsensor electrode and the at least one display electrode during the firstperiod.

Another embodiment described herein is a method for mitigating an effectof a coupling capacitance associated with a display electrode whenperforming capacitive sensing. The method driving a modulated signalonto a first sensor electrode of a plurality of sensor electrodes todetect a change in capacitive coupling between an input object and thefirst sensor electrode during a first period. The method also includesoperating the display electrode in a guard mode to mitigate the effectof the coupling capacitance between the first sensor electrode and thedisplay electrode during the first period.

Another embodiment described herein is a processing system for an inputdevice. The processing system includes a display driver modulecomprising display driver circuitry coupled to at least one displayelectrode and configured to drive the at least one display electrode toset a voltage associated with a pixel of a display device and operatethe at least one display electrode in a guard mode to mitigate theeffect of the coupling capacitance between a first sensor electrode of aplurality of sensor electrodes and the at least one display electrodeduring a first time period. During the first time period, the firstsensor electrode is driven with a modulated signal to detect a change incapacitance between the first sensor electrode and an input object.

Another embodiment described herein is a processing system for an inputdevice. The processing system includes a sensor module comprising sensorcircuitry and is coupled to a plurality of sensor electrodes. The sensormodule is configured to drive, during a first time period, one of theplurality of sensor electrodes with a modulated signal to detect achange in capacitive coupling between the one sensor electrode and aninput object. The sensor module is coupled to and synchronized with adisplay driver module that is configured to operate at least one displayelectrode in a guard mode to mitigate the effect of a couplingcapacitance between the one sensor electrode and the at least onedisplay electrode during the first time period.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1A is a schematic block diagram of an input device integrated intoan exemplary display device, according to an embodiment describedherein.

FIGS. 1B-1G illustrate various capacitances in input devices, accordingto embodiments described herein.

FIGS. 2A-2F illustrate circuit models for measuring capacitance,according to embodiments described herein.

FIGS. 3A-3B are schematic block diagrams of a display system forguarding display electrodes during capacitive sensing, according to anembodiment described herein.

FIGS. 4A-4B illustrate an integrated touch and display controller forguarding gate electrodes in the display system, according to anembodiment described herein.

FIG. 5 is a schematic block diagram of a display system where displayelectrodes are used for performing capacitive sensing, according to anembodiment described herein.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may be beneficially utilized on other embodiments withoutspecific recitation. The drawings referred to here should not beunderstood as being drawn to scale unless specifically noted. Also, thedrawings are often simplified and details or components omitted forclarity of presentation and explanation. The drawings and discussionserve to explain principles discussed below, where like designationsdenote like elements.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Furthermore, there is no intention to be bound by anyexpressed or implied theory presented in the preceding technical field,background, brief summary or the following detailed description.

Various embodiments of the present technology provide input devices andmethods for improving usability.

An input device may include sensor electrodes that are used as sensingelements to detect interaction between the input device and an inputobject (e.g., a stylus or a user's finger). To do so, the input devicemay drive a capacitive sensing signal onto the sensor electrodes. Basedon measuring capacitances associated with driving the capacitive sensingsignal, the input device determines a location of user interaction withthe input device. In one embodiment, the electrodes may be locatedproximate to other electrodes in the input device. For example, theinput device may include a display screen for outputting an image to theuser. The sensor electrodes may be mounted on top of the display screenor integrated into a layer or layers within the screen. The variousdisplay electrodes used by the display screen to update the image (e.g.,source electrodes, gate electrodes, common electrodes, etc.), maycapacitively couple to the sensor electrode. This coupling capacitancemay cause the input device to measure the capacitance not associatedwith the input object when driving the capacitive sensing signal ontothe electrode. This extra capacitance can consume system dynamic rangeand limit sensitivity to changes in capacitance due to the input object.This undesired extra capacitance can also change due to environmentalfactors such as image content or sensor temperature such that changes inthe system background capacitance could be erroneously interpreted aschanges from the input object and result in erroneous processingresults.

Transmitting a guarding signal on display electrodes as well as on thesensor electrodes currently not being used to make a capacitivemeasurement may mitigate the effect of this coupling capacitance whenmeasuring capacitance associated with a sensor electrode as well asreduce power consumption or improve settling time. In one embodiment,the guarding signal (or guard signal) may have similar characteristics(e.g., similar amplitude, frequency, or phase) as the capacitive sensingsignal (modulated signal or transmitter signal). By driving a guardingsignal that is similar to the capacitive sensing signal onto the displayelectrodes, the voltage difference between the sensor electrode anddisplay electrodes remains the same. Accordingly, the couplingcapacitance between the electrodes does not affect the capacitancemeasurement obtained during capacitive sensing. In one embodiment, theguarding signal has an amplitude that is greater than that of thecapacitive sensing signal (transmitter signal or modulate signal). Inanother embodiment, the guarding signal has an amplitude that is lessthan that of the capacitive sensing signal (transmitter signal ormodulated signal).

FIG. 1A is a schematic block diagram of an input device 100 integratedinto an exemplary display device 160, in accordance with embodiments ofthe present technology. Although the illustrated embodiments of thepresent disclosure are shown integrated with a display device, it iscontemplated that the invention may be embodied in input devices thatare not integrated with display devices. The input device 100 may beconfigured to provide input to an electronic system 150. As used in thisdocument, the term “electronic system” (or “electronic device”) broadlyrefers to any system capable of electronically processing information.Some non-limiting examples of electronic systems include personalcomputers of all sizes and shapes, such as desktop computers, laptopcomputers, netbook computers, tablets, web browsers, e-book readers, andpersonal digital assistants (PDAs). Additional example electronicsystems include composite input devices, such as physical keyboards thatinclude input device 100 and separate joysticks or key switches. Furtherexample electronic systems include peripherals such as data inputdevices (including remote controls and mice), and data output devices(including display screens and printers). Other examples include remoteterminals, kiosks, and video game machines (e.g., video game consoles,portable gaming devices, and the like). Other examples includecommunication devices (including cellular phones, such as smart phones),and media devices (including recorders, editors, and players such astelevisions, set-top boxes, music players, digital photo frames, anddigital cameras). Additionally, the electronic system could be a host ora slave to the input device.

The input device 100 can be implemented as a physical part of theelectronic system, or can be physically separate from the electronicsystem. As appropriate, the input device 100 may communicate with partsof the electronic system using any one or more of the following: buses,networks, and other wired or wireless interconnections. Examples includeI²C, SPI, PS/2, Universal Serial Bus (USB), Bluetooth, RF, and IRDA.

In FIG. 1A, the input device 100 is shown as a proximity sensor device(also often referred to as a “touchpad” or a “touch sensor device”)configured to sense input provided by one or more input objects 140 in asensing region 170. Example input objects include fingers and styli, asshown in FIG. 1A.

Sensing region 170 encompasses any space above, around, in and/or nearthe input device 100 in which the input device 100 is able to detectuser input (e.g., user input provided by one or more input objects 140).The sizes, shapes, and locations of particular sensing regions may varywidely from embodiment to embodiment. In some embodiments, the sensingregion 170 extends from a surface of the input device 100 in one or moredirections into space until signal-to-noise ratios prevent sufficientlyaccurate object detection. The distance to which this sensing region 170extends in a particular direction, in various embodiments, may be on theorder of less than a millimeter, millimeters, centimeters, or more, andmay vary significantly with the type of sensing technology used and theaccuracy desired. Thus, some embodiments sense input that comprises nocontact with any surfaces of the input device 100, contact with an inputsurface (e.g. a touch surface) of the input device 100, contact with aninput surface of the input device 100 coupled with some amount ofapplied force or pressure, and/or a combination thereof. In variousembodiments, input surfaces may be provided by surfaces of casingswithin which the sensor electrodes reside, by face sheets applied overthe sensor electrodes or any casings, etc. In some embodiments, thesensing region 170 has a rectangular shape when projected onto an inputsurface of the input device 100.

The input device 100 may utilize any combination of sensor componentsand sensing technologies to detect user input in the sensing region 170.The input device 100 comprises a plurality of sensing 120 for detectinguser input. The input device 100 may include one or more sensingelements 120 that are combined to form sensor electrodes. As severalnon-limiting examples, the input device 100 may use capacitive,elastive, resistive, inductive, magnetic acoustic, ultrasonic, and/oroptical techniques.

Some implementations are configured to provide images that span one,two, three, or higher dimensional spaces. Some implementations areconfigured to provide projections of input along particular axes orplanes.

In some resistive implementations of the input device 100, a flexibleand conductive first layer is separated by one or more spacer elementsfrom a conductive second layer. During operation, one or more voltagegradients are created across the layers. Pressing the flexible firstlayer may deflect it sufficiently to create electrical contact betweenthe layers, resulting in voltage outputs reflective of the point(s) ofcontact between the layers. These voltage outputs may be used todetermine positional information.

In some inductive implementations of the input device 100, one or moresensing elements 120 pickup loop currents induced by a resonating coilor pair of coils. Some combination of the magnitude, phase, andfrequency of the currents may then be used to determine positionalinformation.

In some capacitive implementations of the input device 100, voltage orcurrent is applied to create an electric field. Nearby input objectscause changes in the electric field, and produce detectable changes incapacitive coupling that may be detected as changes in voltage, current,or the like.

Some capacitive implementations utilize arrays or other regular orirregular patterns of capacitive sensing elements 120 to create electricfields. In some capacitive implementations, separate sensing elements120 may be ohmically shorted together to form larger sensor electrodes.Some capacitive implementations utilize resistive sheets, which may beuniformly resistive.

As discussed above, some capacitive implementations utilize “selfcapacitance” (or “absolute capacitance”) sensing methods based onchanges in the capacitive coupling between sensor electrodes 120 and aninput object. In one embodiment, processing system 110 is configured todrive a voltage with known amplitude onto the sensor electrode 120 andmeasure the amount of charge required to charge the sensor electrode tothe driven voltage. In other embodiments, processing system 110 isconfigured to drive a known current and measure the resulting voltage.In various embodiments, an input object near the sensor electrodes 120alters the electric field near the sensor electrodes 120, thus changingthe measured capacitive coupling. In one implementation, an absolutecapacitance sensing method operates by modulating sensor electrodes 120with respect to a reference voltage (e.g. system ground) using amodulated signal, and by detecting the capacitive coupling between thesensor electrodes 120 and input objects 140.

Additionally as discussed above, some capacitive implementations utilize“mutual capacitance” (or “transcapacitance”) sensing methods based onchanges in the capacitive coupling between sensing electrodes. Invarious embodiments, an input object 140 near the sensing electrodesalters the electric field between the sensing electrodes, thus changingthe measured capacitive coupling. In one implementation, atranscapacitive sensing method operates by detecting the capacitivecoupling between one or more transmitter sensing electrodes (also“transmitter electrodes”) and one or more receiver sensing electrodes(also “receiver electrodes”) as further described below. Transmittersensing electrodes may be modulated relative to a reference voltage(e.g., system ground) to transmit a transmitter signals. Receiversensing electrodes may be held substantially constant relative to thereference voltage to facilitate receipt of resulting signals. Aresulting signal may comprise effect(s) corresponding to one or moretransmitter signals, and/or to one or more sources of environmentalinterference (e.g. other electromagnetic signals). Sensing electrodesmay be dedicated transmitter electrodes or receiver electrodes, or maybe configured to both transmit and receive.

In FIG. 1A, the processing system 110 is shown as part of the inputdevice 100. The processing system 110 is configured to operate thehardware of the input device 100 to detect input in the sensing region170. The processing system 110 comprises parts of or all of one or moreintegrated circuits (ICs) and/or other circuitry components. (Forexample, a processing system for a mutual capacitance sensor device maycomprise transmitter circuitry configured to transmit signals withtransmitter sensor electrodes, and/or receiver circuitry configured toreceive signals with receiver sensor electrodes). In some embodiments,the processing system 110 also comprises electronically-readableinstructions, such as firmware code, software code, and/or the like. Insome embodiments, components composing the processing system 110 arelocated together, such as near sensing element(s) 120 of the inputdevice 100. In other embodiments, components of processing system 110are physically separate with one or more components close to sensingelement(s) 120 of input device 100, and one or more componentselsewhere. For example, the input device 100 may be a peripheral coupledto a desktop computer, and the processing system 110 may comprisesoftware configured to run on a central processing unit of the desktopcomputer and one or more ICs (perhaps with associated firmware) separatefrom the central processing unit. As another example, the input device100 may be physically integrated in a phone, and the processing system110 may comprise circuits and firmware that are part of a main processorof the phone. In some embodiments, the processing system 110 isdedicated to implementing the input device 100. In other embodiments,the processing system 110 also performs other functions, such asoperating display screens, driving haptic actuators, etc.

The processing system 110 may be implemented as a set of modules thathandle different functions of the processing system 110. Each module maycomprise circuitry that is a part of the processing system 110,firmware, software, or a combination thereof. In various embodiments,different combinations of modules may be used. Example modules includehardware operation modules for operating hardware such as sensorelectrodes and display screens, data processing modules for processingdata such as sensor signals and positional information, and reportingmodules for reporting information. Further example modules includesensor operation modules configured to operate sensing elements 120 todetect input, identification modules configured to identify gesturessuch as mode changing gestures, and mode changing modules for changingoperation modes. Processing system 110 may also comprise one or morecontrollers.

In some embodiments, the processing system 110 responds to user input(or lack of user input) in the sensing region 170 directly by causingone or more actions. Example actions include changing operation modes,as well as GUI actions such as cursor movement, selection, menunavigation, and other functions. In some embodiments, the processingsystem 110 provides information about the input (or lack of input) tosome part of the electronic system (e.g. to a central processing systemof the electronic system that is separate from the processing system110, if such a separate central processing system exists). In someembodiments, some part of the electronic system processes informationreceived from the processing system 110 to act on user input, such as tofacilitate a full range of actions, including mode changing actions andGUI actions.

For example, in some embodiments, the processing system 110 operates thesensing element(s) 120 of the input device 100 to produce electricalsignals indicative of input (or lack of input) in the sensing region170. The processing system 110 may perform any appropriate amount ofprocessing on the electrical signals in producing the informationprovided to the electronic system. For example, the processing system110 may digitize analog electrical signals obtained from the sensingelements 120. As another example, the processing system 110 may performfiltering or other signal conditioning. As yet another example, theprocessing system 110 may subtract or otherwise account for a baseline,such that the information reflects a difference between the electricalsignals and the baseline. As yet further examples, the processing system110 may determine positional information, recognize inputs as commands,recognize handwriting, and the like.

“Positional information” as used herein broadly encompasses absoluteposition, relative position, velocity, acceleration, and other types ofspatial information. Exemplary “zero-dimensional” positional informationincludes near/far or contact/no contact information. Exemplary“one-dimensional” positional information includes positions along anaxis. Exemplary “two-dimensional” positional information includesmotions in a plane. Exemplary “three-dimensional” positional informationincludes instantaneous or average velocities in space. Further examplesinclude other representations of spatial information. Historical dataregarding one or more types of positional information may also bedetermined and/or stored, including, for example, historical data thattracks position, motion, or instantaneous velocity over time.

In some embodiments, the input device 100 is implemented with additionalinput components that are operated by the processing system 110 or bysome other processing system. These additional input components mayprovide redundant functionality for input in the sensing region 170, orsome other functionality. FIG. 1A shows buttons 130 near the sensingregion 170 that can be used to facilitate selection of items using theinput device 100. Other types of additional input components includesliders, balls, wheels, switches, and the like. Conversely, in someembodiments, the input device 100 may be implemented with no other inputcomponents.

In some embodiments, the input device 100 comprises a touch screeninterface, and the sensing region 170 overlaps at least part of anactive area of a display screen of the display device 160. For example,the input device 100 may comprise substantially transparent sensingelements 120 overlaying the display screen and provide a touch screeninterface for the associated electronic system. The display screen maybe any type of dynamic display capable of displaying a visual interfaceto a user, and may include any type of light emitting diode (LED),organic LED (OLED), cathode ray tube (CRT), liquid crystal display(LCD), plasma, electroluminescence (EL), or other display technology.The input device 100 and the display device 160 may share physicalelements. For example, some embodiments may utilize some of the sameelectrical components for displaying and sensing. As another example,the display device 160 may be operated in part or in total by theprocessing system 110.

It should be understood that while many embodiments of the presenttechnology are described in the context of a fully functioningapparatus, the mechanisms of the present technology are capable of beingdistributed as a program product (e.g., software) in a variety of forms.For example, the mechanisms of the present technology may be implementedand distributed as a software program on information bearing media thatare readable by electronic processors (e.g., non-transitorycomputer-readable and/or recordable/writable information bearing mediareadable by the processing system 110). Additionally, the embodiments ofthe present technology apply equally regardless of the particular typeof medium used to carry out the distribution. Examples ofnon-transitory, electronically readable media include various discs,memory sticks, memory cards, memory modules, and the like.Electronically readable media may be based on flash, optical, magnetic,holographic, or any other storage technology.

Guarding Signals

Absolute capacitive sensing may be performed by measuring thecapacitance from a sensor electrode to substantially constant voltage(i.e., system ground or any other substantially constant voltage). FIGS.1B-1G illustrate a network containing four nodes—A, B, C, and GND—thatmay be used when performing capacitive sensing. FIG. 1B, for instance,illustrates the various capacitances that may exist in a networkcontaining these four nodes. As shown, there are six capacitancesillustrated in this four-node network. Figure 1B (as it is driven by amodulated signal), any one of the nodes A, B or C may be used as asensor electrode. In FIG. 1B, the sensor electrode (node A) has acapacitance, C_(F), to GND, in parallel with C_(A). The capacitanceC_(F) changes based on the proximity of an input object to the sensorelectrode. Thus by measuring C_(F), the position of the proximate inputobject may be determined. Throughout this description, node A and sensorelectrode may be used interchangeably.

In one embodiment, the changed capacitance from a sensor electrode to aproximate input object is measured by driving a modulated signal(illustrated as V(t)) onto the sensor electrode and then measuring theresulting signals received with the sensor electrode. In one embodimentthe resulting signals correspond to a resulting current, i(t). Bymeasuring the resulting signals, the position of the input object may bedetermined. However, the capacitances C_(A), C_(AB), C_(CA), C_(B),C_(BC) and/or C_(C) shown in FIG. 1B may have several deleteriouseffects. For example, the total capacitance of the sensor electrode toground is increased, increasing the settling time of the sensorelectrode and the magnitude of the capacitances in the resulting signalis also increased which increases the required dynamic range of thesensing circuit. In various embodiments, some of the capacitances may bevariable (due to process, temperature, applied DC voltage, etc.), makingit difficult to compensate for the variation. In many embodiments,reducing or removing the other capacitances will improve performance ofthe input device and may make the change in capacitance between an inputobject and the sensor electrode more easily determined.

In one embodiment, and with further reference to FIG. 1B, thecapacitance C_(F) may be determined by driving node A, the sensorelectrode, with a modulated signal and measuring a received resultingsignal. During this drive and measurement phase, node B (i.e., anotherelectrode) may be left floating, driven with a substantially constantvoltage (e.g., ground, etc.) or driven with a guarding signal.Similarly, node C may be left floating, driven with a substantiallyconstant voltage (ground) or driven with the guarding signal. Thus,there are nine possible combinations for nodes/electrodes B and C duringthe measurement as illustrated by Table 1 below.

TABLE 1 Combination Number Description Node B Node C 1 No Guarding,Electrodes Grounded grounded grounded 2 No Guarding, FloatingElectrodes. floated floated 3 Guard by driving electrodes B and GuardedGuarded C with a guard signal 4 Drive electrode B with a guard Guardedfloated signal and float electrode C 5 Drive electrode B with a guardGuarded grounded signal and ground electrode C 6 Ground electrode C andfloat floated grounded electrode B. 7 Guard Electrode C while groundedGuarded Grounding Electrode B 8 Guard Electrode C while Floating floatedGuarded Electrode B 9 Ground Electrode B and Floating grounded floatedElectrode C

Reducing or eliminating the effects of the parasitic capacitancesimproves the settling time of the sensor electrode (node A in FIG. 1B)given the presence of parasitic resistances, which are not shown inFIGS. 1B-1G, allows more measurements per unit of time, and increasesthe signal to noise ratio. Some or all of capacitances C_(A), C_(B),C_(C), C_(AB), C_(BC) and C_(CA) may also vary as a function oftemperature, process, applied voltage or other conditions. Themitigation of this variability is important in order to accuratelydetect changes in capacitance resulting from the input object.

In another embodiment of FIG. 1B, the measurement of C_(F) may beimproved by leaving nodes B and C open (electrically floating nodes Band C) during the measurement of C_(F). If the values of C_(A), C_(B)and C_(C) are small relative to the coupling capacitances C_(BC) andC_(CA) (e.g., an order of magnitude smaller), then guarding one node andfloating the other becomes more effective. If the values of thecapacitances from the nodes to ground are large relative to the couplingcapacitances, however, then floating the node becomes less effective.

In the embodiment shown in FIG. 1C, the capacitance C_(F) may bedetermined by grounding nodes B and C while driving node A with amodulated signal and measuring the resulting signal. Because nodes B andC are grounded, the capacitances C_(AB) and C_(CB) are effectively inparallel with the capacitance C_(F) and C_(A) while C_(B), C_(BC) andC_(C) are effectively removed from the circuit (as shown by the dashedboxes). Capacitances C_(AB) and C_(CB) are typically large with respectto C_(F), which increases the required dynamic range of the receivermodule since C_(F) along with C_(AB) and C_(CB) are all measured.Furthermore, because capacitances C_(AB) and C_(CB) are distributedcapacitances along the resistive sensor electrode, the settling time ofthe sensor electrode is also increased.

Alternatively, as shown in FIG. 1D, nodes B and C (electrodes B and C)are both “guarded” by driving a guarding signal at the nodes shown bythe two V(t) voltage generators. The guarding signal may be equal to themodulated signal V(t) in at least one of amplitude, shape, phase and/orfrequency. In such embodiments, the voltages across all of the couplingcapacitances C_(AB), C_(BC) and C_(CA) shown in FIG. 1D that areconnected to nodes B and C do not change, and thus, these capacitancesare effectively removed from the circuit. The measured capacitance isthe sum of C_(F) with the single capacitance C_(A). In many embodiments,C_(A) is on the same order as C_(F), and as such the dynamic range ofthe receiver module may not need to be increased and/or the settlingtime of the sensor electrode is only slightly increased due to C_(A),allowing higher modulated signal or transmitter signal frequencies to beused. The guarding also has the important secondary benefit of removingthe effects of changes in capacitors C_(AB), C_(BC) and C_(CA) due totemperature, voltage, etc.

In some embodiments, as illustrated in FIG. 1E, a guarding signal isapplied to one of node B and C while other node B or C is electricallyfloated. In this particular embodiment, the guarding signal is appliedto node B as shown by shown by the V(t) voltage generator. Thecapacitance C_(C) is assumed to be small compared to C_(BC) and C_(CA),thus node C is effectively driven by the guarding signal applied to nodeB. This effectively removes C_(CA) from the circuit. Further, since amodulated signal and a guarding signal is applied to both ends of theseries combination of C_(BC) and C_(CA), capacitors C_(BC) and C_(CA)may also be substantially eliminated from the equivalent circuit. Thus,when C_(C) is small compared to C_(BC) and C_(CA), guarding onlynode/electrode B while floating node/electrode C may be substantiallyequivalent to guarding both nodes/electrodes B and C.

In the embodiment illustrated in FIG. 1F, a guard signal is driven ontonode B or node C while the other one of node B or node C is driven witha substantially constant voltage (i.e., grounded). Because node B isdriven, capacitance C_(B) does not substantially affect the resultingsignal, and since one end of C_(BC) is driven and the other is grounded,C_(BC) does not substantially affect the resulting signal. Further,since node C is grounded, capacitance C_(C) does not substantiallyaffect the resulting signal. Further, because both ends of C_(AB) aredriven in with a similar signal, it does not affect the resultingsignal. However, since node C is driven with a substantially constantvoltage and since node A is driven with the modulated signal, thecapacitance between node C and node A (C_(CA)) may affect the resultingsignal. This embodiment is different from FIGS. 1D and 1E in that, forexample, the capacitance value between the nodes and ground (e.g.,C_(C)) is removed while the coupling capacitance (e.g., C_(CA)) is not.

FIG. 1G illustrates an embodiment where one of node B and node C isgrounded and the other one of the nodes is floated. In the illustratedembodiment, since node B is grounded, capacitance C_(B) does not affectthe resulting signal. Further, since C_(C) and C_(BC) are in paralleland C_(C) is, in many embodiments, smaller than C_(BC), C_(C) may beignored. This results in C_(AB), C_(A), and C_(CA) in series with C_(BC)which may affect the resulting signal.

In one embodiment of a display device, there are typically threeelectrodes that are shared by the pixels, for example: Vcom electrode(common electrode(s)), gate electrodes (gate lines) and sourceelectrodes (source lines). As will be discussed in more detail below, invarious embodiments, any of these electrodes may be configured as asensor electrode. In one embodiment, the four node network described inFIGS. 1B-1G may correspond to a single sub-pixel; however, a similardiscussion may be extended to an aggregated group of sub-pixels. Forexample, node A may be a sensor electrode that is also used in updatinga display. Nodes B and C may be other types of display electrodes (e.g.,gate and source electrodes). Further, the capacitances associated with asensor electrode may also include the capacitances of the associatedwiring or other routing. The capacitances associated with a sub-pixelmay include a network containing the four nodes: AC system ground (alsoreferred to as “GND” and shown by the symbol

in the various figures), Vcom electrodes, source electrodes and gateelectrodes.

In one embodiment, each of the sensor electrodes comprise one or moresegments of the common electrode layer (Vcom electrode segments), sourcelines and gate lines, where a sensor electrode corresponds to node A andthe source lines correspond to node B and the gate lines correspond tonode C in the above discussion. The source lines and/or gate lines maybe driven with a guarding signal or electrically floated to at leastpartially remove their parasitic capacitance effects. Further, commonelectrodes may also be driven with guarding signal so that theircapacitances will not affect the sensor electrode that is being drivenfor capacitive sensing. In contrast, typical display devices may drive aDC voltage on the source and gate lines during the touch measurementinterval as shown in, for example, FIG. 1C where node B and node C aregrounded. In contrast, FIGS. 1D-1F illustrate driving guarding signalsonto at least one of the display electrodes in order to remove one ormore of the coupling capacitances.

In another embodiment, the sensor electrodes are separate from the Vcomelectrode(s) (common electrodes), where the Vcom electrode is drivenwith a guarding signal to reduce the effects of the parasitic capacitivecoupling between the Vcom electrode and the sensor electrodes. Further,all of the gate lines and/or source lines may also be driven with aguarding signal or electrically floated to reduce the parasiticcapacitance effects between the gate lines and the sensor electrodes andthe source lines and sensor electrodes.

In a further embodiment, a first sensor electrode may be driven with atransmitter signal while a resulting signal comprising effectscorresponding to the transmitter signal is received with a second sensorelectrode. Similar schemes as described above may be applied to displayelectrodes proximate the first sensor electrode and/or second sensorelectrode. By, reducing or eliminating the capacitances to ground fromthe transmitter electrode (first sensor electrode) and the receiverelectrode (second sensor electrode) the settling time of the transmitterelectrode and/or receiver electrodes may be improved. Further, anyvariations in the capacitance values between the transmitter andreceiver electrodes based on the variations in the capacitances betweenthe transmitter and/or receiver electrodes and the display electrodesmay be reduced or eliminated.

The above discussion may be further applied to the variousconfigurations embodied in the forthcoming description.

Sensor Electrode Arrangements

In one embodiment, the sensor electrodes 120 may be arranged ondifferent sides of the same substrate. For example, each of the sensorelectrode(s) 120 may extend longitudinally across one of the surfaces ofthe substrate. Further still, on one side of the substrate, the sensorelectrodes 120 may extend in a first direction, but on the other side ofthe substrate, the sensor electrodes 120 may extend in a seconddirection that is either parallel with, or perpendicular to, the firstdirection. For example, the electrodes 120 may be shaped as bars orstripes where the electrodes 120 on one side of the substrate extend ina direction perpendicular to the sensor electrodes 120 on the oppositeside of the substrate.

The sensor electrodes may be formed into any desired shape on the sidesof the substrate. Moreover, the size and/or shape of the sensorelectrodes 120 on one side of the substrate may be different than thesize and/or size of the electrodes 120 on another side of the substrate.Additionally, the sensor electrodes 120 on the same side may havedifferent shapes and sizes.

In another embodiment, the sensor electrodes 120 may be formed ondifferent substrates that are then laminated together. In one example, afirst plurality of the sensor electrodes 120 disposed on one of thesubstrate may be used to transmit a sensing signal (i.e., transmitterelectrodes) while a second plurality of the sensor electrodes 120disposed on the other substrate are used to receive resulting signals(i.e., receiver electrodes). In other embodiments, the first and/orsecond plurality of sensor electrodes may be driven as absolutecapacitive sensor electrodes. In one embodiment, the first plurality ofsensor electrodes may be larger (larger surface area) than the secondplurality of sensor electrodes, although this is not a requirement. Inother embodiments, the first plurality and second plurality of sensorelectrodes may have a similar size and/or shape. Thus, the size and/orshape of the sensor electrodes 120 on one of the substrates may bedifferent than the size and/or size of the electrodes 120 on the othersubstrate. Nonetheless, the sensor electrodes 120 may be formed into anydesired shape on their respective substrates. Additionally, the sensorelectrodes 120 on the same substrate may have different shapes andsizes.

In another embodiment, the sensor electrodes 120 are all located on thesame side or surface of a common substrate. In one example, a firstplurality of the sensor electrodes comprise jumpers in regions where thefirst plurality of sensor electrodes crossover the second plurality ofsensor electrodes, where the jumpers are insulated from the secondplurality of sensor electrodes. As above, the sensor electrodes 120 mayeach have the same size or shape or differing size and shapes.

In another embodiment, the sensor electrodes 120 are all located on thesame side or surface of the common substrate are isolated from eachother in the sensing region 170. In such embodiments, the sensorelectrodes 120 are electrically isolated from each other. In oneembodiment, the electrodes 120 are disposed in a matrix array where eachsensor electrode 120 is substantially the same size and/or shape. Insuch embodiment, the sensor electrodes 120 may be referred to as amatrix sensor electrode. In one embodiment, one or more of sensorelectrodes of the matrix array of sensor electrodes 120 may vary in atleast one of size and shape. Each sensor electrode of the matrix arraymay correspond to a pixel of the capacitive image. In one embodiment,the processing system 110 is configured to drive the sensor electrodes120 with a modulated signal to determine changes in absolutecapacitance. In other embodiment, processing system 110 is configured todrive a transmitter signal onto a first one of the sensor electrodes 120and receive a resulting signal with a second one of the sensorelectrodes 120. The transmitter signal(s) and modulated signal(s) may besimilar in at least one of shape, amplitude, frequency and phase. Invarious embodiments, the transmitter signal(s) and modulated signal(s)are the same signal. Further, the transmitter signal is a modulatedsignal that is used to for transcapactive sensing. In variousembodiments, one or more grid electrodes may be disposed on the commonsubstrate, between the sensor electrodes 120 where the grid electrode(s)may be used to shield and guard the sensor electrodes.

As used herein, shielding refers to driving a constant voltage onto anelectrode and guarding refers to driving a varying voltage signal onto asecond electrode that is substantially similar in amplitude and phase tothe signal modulating the first electrode in order to measure thecapacitance of the first electrode. Electrically floating an electrodecan be interpreted as a form of guarding in cases where, by floating,the second electrode receives the desired guarding waveform viacapacitive coupling from the first or third electrode in the inputdevice 100. In various embodiments, guarding may be considered to be asubset of shielding such that guarding a sensor electrode would alsoshield that sensor electrode. The grid electrode may be driven with avarying voltage, a substantially constant voltage or be electricallyfloated. The grid electrode may also be used as a transmitter electrodewhen it is driven with a transmitter signal such that the capacitivecoupling between the grid electrode and one or more sensor electrodesmay be determined. In one embodiment, a floating electrode may bedisposed between the grid electrode and the sensor electrodes. In oneparticular embodiment, the floating electrode, the grid electrode andthe sensor electrode comprise the entirety of a common electrode of adisplay device. In other embodiments, the grid electrode may be disposedon a separate substrate or surface of a substrate than the sensorelectrodes 120 or both. Although the sensor electrodes 120 may beelectrically isolated on the substrate, the electrodes may be coupledtogether outside of the sensing region 170—e.g., in a connection regionthat transmits or receives capacitive sensing signals on the sensorelectrodes 120. In various embodiments, the sensor electrodes 120 may bedisposed in an array using various patterns where the electrodes 120 arenot all the same size and shape. Furthermore, the distance between theelectrodes 120 in the array may not be equidistant.

In any of the sensor electrode arrangements discussed above, the sensorelectrodes 120 and/or grid electrode(s) may be formed on a substratethat is external to the display device 160. For example, the electrodes120 and/or grid electrode(s) may be disposed on the outer surface of alens in the input device 100. In other embodiments, the sensorelectrodes 120 and/or grid electrode(s) are disposed between the colorfilter glass of the display device and the lens of the input device. Inother embodiments, at least a portion of the sensor electrodes and/orgrid electrode(s) may be disposed such that they are between a Thin FilmTransistor substrate (TFT substrate) and the color filter glass of thedisplay device 160. In one embodiment, a first plurality of sensorelectrodes and/or grid electrode(s) are disposed between the TFTsubstrate and color filter glass of the display device 160 and thesecond plurality of sensor electrodes and/or a second grid electrode(s)are disposed between the color filter glass and the lens of the inputdevice 100. In yet other embodiments, all of sensor electrodes 120and/or grid electrode(s) are disposed between the TFT substrate andcolor filter glass of the display device, where the sensor electrodesmay be disposed on the same substrate or on different substrates asdescribed above.

In one or more embodiment, at least a first plurality the sensorelectrodes 120 comprised one or more display electrodes of the displaydevice that are used in updating the display. For example, the sensorelectrodes 120 may comprise the common electrodes such as one or moresegments of a Vcom electrode, a source drive line, gate line, an anodesub-pixel electrode or cathode pixel electrode, or any other displayelement. These common electrodes may be disposed on an appropriatedisplay screen substrate. For example, the common electrodes may bedisposed on a transparent substrate (a glass substrate, TFT glass, orany other transparent material) in some display screens (e.g., In PlaneSwitching (IPS), Fringe Field Switching (FFS) or Plane to Line Switching(PLS) Organic Light Emitting Diode (OLED)), on the bottom of the colorfilter glass of some display screens (e.g., Patterned Vertical Alignment(PVA) Multi-domain Vertical Alignment (MVA), IPS and FFS), over ancathode layer (OLED), etc. In such embodiments, the common electrode canalso be referred to as a “combination electrode”, since it performsmultiple functions. In various embodiments, each of the sensorelectrodes 120 comprises one or more common electrodes associated with apixel or sub pixel. In other embodiments, at least two sensor electrodes120 may share at least one common electrode associated with a pixel orsub-pixel. While the first plurality sensor electrodes may comprise oneor more common electrodes configured for display updating and capacitivesensing, the second plurality of sensor electrodes may be configured forcapacitive sensing and not for display updating. Further, in one or moreembodiments, the grid electrode and/or floating electrode, when present,comprises one or more common electrodes.

Alternatively, all of the sensor electrodes 120 may be disposed betweenthe TFT substrate and the color filter glass of the display device 160.In one embodiment, a first plurality of sensor electrodes are disposedon the TFT substrate, each comprising one or more common electrodes anda second plurality of sensor electrodes may be disposed between thecolor filter glass and the TFT substrate. Specifically, the receiverelectrodes may be routed within the black mask on the color filterglass. In another embodiment, all of the sensor electrodes 120 compriseone or more common electrodes. The sensor electrodes 120 may be locatedentirely on the TFT substrate or the color filter glass as an array ofelectrodes. As discussed above, some of the sensor electrodes 120 may becoupled together in the array using jumper or all the electrodes 120 maybe electrically isolated in the array and use grid electrodes to shieldor guard the sensor electrodes 120. In one more embodiments, the gridelectrode, when present, comprises one or more common electrodes.

In any of the sensor electrode arrangements described above, the sensorelectrodes 120 may be operated in the input device 100 in thetranscapacitive mode by dividing the sensor electrodes 120 intotransmitter and receiver electrodes or in the absolute capacitivesensing mode, or some mixture of both.

As will be discussed in more detail below, one or more of the sensorelectrodes 120 or the display electrodes (e.g., source, gate, orreference (common) lines) may be used to perform shielding or guarding.As used herein, shielding refers to driving a constant voltage or aguard signal (varying voltage signal) onto an electrode as well asfloating an electrode in the input device 100.

Continuing to refer to FIG. 1A, the processing system 110 coupled to thesensor electrodes 120 includes a sensor module and in variousembodiments, processing system 110 may also or alternatively comprise adisplay driver module. The sensor module includes circuitry configuredto drive at least one of the sensor electrodes 120 for capacitivesensing during periods in which input sensing is desired. In oneembodiment, the sensor module is configured to drive a modulated signalonto the at least one sensor electrode to detect changes in absolutecapacitance between the at least one sensor electrode and an inputobject. In another embodiment, the sensor module is configured to drivea transmitter signal onto the at least one sensor electrode to detectchanges in a transcapacitance between the at least one sensor electrodeand another sensor electrode. The modulated and transmitter signals aregenerally varying voltage signals comprising a plurality of voltagetransitions over a period of time allocated for input sensing and mayalso be referred to as a capacitive sensing signal. In variousembodiments, the modulated signal and transmitter signal are similar inat least one shape, frequency, amplitude and/or phase. In otherembodiments, the modulated signal and the transmitter signals aredifferent in frequency, shape, phase, amplitude and phase. The sensormodule may be selectively coupled to one or more of the sensorelectrodes 120. For example, the sensor module 204 may be coupled to atleast one of the sensor electrodes 120 and operate in either an absoluteor transcapacitive sensing mode.

The sensor module includes circuitry configured to receive resultingsignals with the sensor electrodes 120 comprising effects correspondingto the modulated signals or the transmitter signals during periods inwhich input sensing is desired. The sensor module may determine aposition of the input object 140 in the sensing region or may provide asignal including information indicative of the resulting signal toanother module or processor, for example, determination module or aprocessor of the electronic device (i.e., a host processor), fordetermining the position of the input object 140 in the sensing region.

The display driver module includes circuitry configured to providedisplay image update information to the display of the display device160 during display updating periods. In one embodiment, the displaydriver is coupled to the display electrodes (source electrodes, gateelectrodes and Vcom electrodes) configured to drive at least one displayelectrode to set a voltage associated with a pixel of a display device,and operate the at least one display electrode in a guard mode tomitigate the effect of the coupling capacitance between a first sensorelectrode of a plurality of sensor electrodes and the at least onedisplay electrode. In various embodiments, the display electrode is atleast one of a source electrode that drives a voltage onto a storageelement associated with the pixel, a gate electrode that sets a gatevoltage on a transistor associated with the pixel, and a commonelectrode that provides a reference voltage to the storage element.

In one embodiment, the sensor module and display driver module may becomprised within a common integrated circuit (first controller). Inanother embodiment, the sensor module and display driver module arecomprised in two separate integrated circuits. In those embodimentscomprising multiple integrated circuits, a synchronization mechanism maybe coupled between them, configured to synchronize display updatingperiods, sensing periods, transmitter signals, display update signalsand the like.

Guarding Display Electrodes

FIGS. 2A-2E are circuit diagrams illustrating circuits for measuringcapacitance, according to embodiments described herein. Specifically,FIGS. 2A-2E may represent the circuit model of the input device 100 inFIG. 1A when performing absolute capacitance sensing as described above.Although the present embodiments discuss using a guarding signal in thecontext of absolute capacitance sensing, the disclosure is not limitedto such. Instead, during transcapacitance sensing, the guarding signal(i.e., a similar signal as the transmitter signal) may be transmitted onthe display electrodes described below that are not used duringcapacitive sensing. Doing so may reduce power consumption and improvesettling time.

As shown by diagram 200 in FIG. 2A, at node D, a sensing voltage iscoupled to one or more of the sensor electrode 120. Diagram 200 includesan integrator 210 comprising an op amp with a feedback capacitor(C_(FB)). The integrator 210 measures the capacitance between the sensorelectrode 120 and free space (or earth ground) which is represented bythe capacitor C_(ABS) in FIG. 2A. This capacitance changes as the inputobject comes within proximity of the sensing area in the input device.In one embodiment, at node E a modulated signal may switch between a lowvoltage and a high voltage. As the voltage at node E changes, theintegrator drives the negative terminal to the same voltage. Based onthe output voltage of the integrator 210, the input device can determinehow much charge had to flow in order to charge the capacitances C_(ABS)and C_(P), and thus, determine the value of these capacitances. In otherembodiments, the modulated voltage may instead be applied at the node Ein order to measure C_(ABS). Further still, instead of driving a voltagein order to measure a current to determine the value of C_(ABS) as shownin FIGS. 2A-2F, alternatively the input device could drive a current andmeasure a voltage. Regardless of the specific technique used to measureC_(ABS), guarding the sensor and/or display electrodes as describedbelow may improve performance.

Diagram 200 also illustrates that a parasitic capacitance C_(P) mayaffect the measurement obtained by the integrator 210. As is describedabove in relation to FIGS. 1B-1G, because the parasitic capacitance maybe much larger than changes in capacitance C_(ABS), the integrator 210may be unable to effectively identify the changes in capacitance C_(ABS)without utilizing techniques to address high parasitic capacitanceC_(P). Diagram 250 in FIG. 2B illustrates a circuit model where aguarding signal 215 is applied that enables the integrator 210 toeffectively identify the change in capacitance C_(ABS) even in thepresence of high parasitic capacitance C_(P).

In diagram 250, and as described above, the parasitic capacitance C_(P)represents the coupling capacitance between a sensor electrode 120 andany electrode 205 in the input device. As such, electrode 205 may beanother sensor electrode that is currently not being sensed or a displayelectrode that is proximate to electrode 120—e.g., a source, Vcom,cathode, or gate electrode used to update a display image in the inputdevice. In order to prevent parasitic capacitance between electrode 205and sensor electrode 120 from interfering with the absolute capacitancemeasurement taken by integrator 210, a guarding signal may be directlyor indirectly applied to the electrode 205. Specifically, the guardingsignal may be the same or substantially similar to the modulating signaldriven on electrode 120. Thus, if the voltage across the parasiticcapacitance does not change (i.e., if the voltage on one side of thecapacitance C_(P) changes by the same amount as the voltage on the otherside) then the capacitance C_(P) does not affect the measurement takenby the integrator 210. For example, if at node E the modulating signalis defined by switching between low and high sensing voltages, the samevoltage change may be applied to the electrode 205 as a guarding signal.

In one embodiment node D or node E may be electrically coupled toelectrode 205 so that the same modulated signal driven on electrode 120is driven as a guarding signal on electrode 205 but this is not arequirement. For example, other driving circuits, which aresynchronized, may be used to drive a guarding signal onto electrode 205that is substantially similar (i.e., same phase and/or frequency and/oramplitude) to the modulated signal driven on electrode 120.

FIG. 2C illustrates a diagram 260 where the sensor electrodes areseparate from the display electrodes (e.g., source, gate, or Vcom (orcathode) electrodes). Because of the close proximity between theelectrodes, there may exist parasitic capacitance between the sensorelectrodes (shown as first sensor electrode in FIG. 2C) and the otherelectrodes in the input device. Stated differently, the parasiticcapacitance in FIG. 2C is the combination of the coupling capacitancebetween a first sensor electrode and a second sensor electrode (C_(SE)),the Vcom electrodes (C_(VCOM)), the source electrodes (C_(S)), and thegate electrodes (C_(G)). In order to mitigate the effect of theseparasitic capacitances when measuring the absolute capacitance, theelectrodes are directly or indirectly driven with one or more guardingsignals.

In one embodiment, the first sensor electrode may be one or more of aplurality of receiver electrodes and the second sensor electrode may oneor more of a plurality of transmitter electrodes. In other embodiments,the first and second sensor electrode is a first and second sensorelectrode of a common plurality of sensor electrodes (e.g., transmitterelectrodes, receiver electrodes, or matrix sensor electrodes). Inanother embodiment, the first sensor electrode may be one or more of aplurality of transmitter electrodes and the second sensor electrode maybe one or more of a plurality of receiver electrodes. In a furtherembodiment, the first sensor electrode is one type of a matrix sensorelectrode and the second sensor electrode is the same type of matrixsensor electrode. In yet a further embodiment, the first sensorelectrode is one or more of a plurality of matrix sensor electrodeswhile the second sensor electrode is one or more grid electrodes.Further, the first sensor electrode is one type of matrix sensorelectrode while the second sensor electrode is a second, different typeof matrix sensor electrode. While not illustrated in FIG. 2C, one of thesecond sensor electrode, the V_(com) electrodes, source electrodes andgate electrodes may be further capacitively coupled to a another sensorelectrode and which may add to the parasitic capacitance of the sensorelectrode.

FIG. 2D illustrates a diagram 270 where a second sensor electrode of thesensor electrodes comprises one or more common electrodes of the displaydevice which are used for display updating (shown here as Vcom/sensorelectrode) and input sensor and first sensor electrode which is not usedfor updating the display device. As illustrated, the first sensorelectrode is capacitively coupled to the Vcom/sensor electrode, sourceelectrode, and gate electrode of the display device. Thus, as themodulated signal is driven on the first sensor electrode, guardingsignal(s) may also be driven onto the Vcom/sensor electrodes, source,and gate electrodes thereby mitigating the effects of the parasiticcapacitance when measuring the absolute capacitance C_(ABS). While notillustrated in FIG. 2D another parasitic capacitance may exist betweenthe first sensor electrode and a second sensor electrode where the firstand second sensor electrodes may be of a common plurality of sensorelectrodes or between the first sensor electrode and a grid electrode.Further, one of the second sensor electrodes, the V_(com) electrodes,source electrodes and gate electrodes may be further capacitivelycoupled to another sensor electrode and which may add to the parasiticcapacitance of the sensor electrode.

In one embodiment, the input device may also measure the absolutecapacitance between the second sensor electrode (Vcom/sensor electrode)and earth ground. In this case, the modulated signal is driven on thesecond sensor electrode while a guarding signal may be driven onto thefirst sensor electrode. Stated differently, instead of driving themodulated signal onto all the sensor electrodes simultaneously, thecircuit performs absolute capacitive sensing on only the second sensorelectrode while driving the guarding signal on the first sensorelectrode during one sensing cycle but then reverses during a subsequentsensing cycle and measures the absolute capacitance associated with thefirst sensor electrode while transmitting the guarding signal on thesecond sensor electrode.

FIG. 2E illustrates a circuit 380 where all of the sensor electrodescomprise one or more common electrodes of the display device. However,in other embodiments, the sensors electrodes may be the source or gateelectrodes. For example, the sensor electrodes may be located on thesame substrate (or surface) as an array of electrodes or distributedacross multiple surfaces in the display device. The parasiticcapacitance between the first sensor electrodes (i.e., common electrodesor Vcom/sensor electrodes) may include the coupling capacitance betweenthe common electrodes and the source, gate, and adjacent sensorelectrodes that are not driven in the same manner as the first sensorelectrode. To ensure that the voltage across these parasiticcapacitances does not change, the guarding signal may be directly orindirectly driven onto source, gate, and adjacent electrodes. Theadjacent sensor electrodes may comprise a grid electrode or a secondsensor electrode. Additionally, the parasitic capacitances between thesensor electrode and additional adjacent sensor electrodes may alsoexist, where the first adjacent sensor electrode may be another sensorelectrode and the second adjacent sensor electrode may be a gridelectrode. Further, one of the adjacent sensor electrodes, sourceelectrodes and gate electrodes may be further capacitively coupled toanother sensor electrode and which may affect the parasitic capacitanceof the sensor electrode.

In a further embodiment, as illustrated in FIG. 2F, a first sensorelectrode (transmitter electrode) may be driven with a transmittersignal while a resulting signal comprising effects corresponding to thetransmitter signal is received with a second sensor electrode (receiverelectrode). In circuit 290, the transmitter electrode comprises at leastone common electrode. Further, the receiver electrode may comprise atleast one common electrode but in various embodiments, the receiverelectrode may be separate from the common electrodes. By, reducing oreliminating the capacitances from the transmitter electrode (firstsensor electrode) to the source/gate electrodes, the settling time ofthe transmitter electrode may be improved. As shown, the sourceelectrodes and/or gate electrodes may be driven with a guarding signalsuch that the parasitic capacitances C_(TS) and C_(TG) between thetransmitter electrode and the source electrodes and/or gate electrodesis reduced or eliminated. While not illustrated in FIG. 2F, anadditional parasitic capacitance may exist between the receiverelectrode and Vcom electrodes when the transmitter electrodes areseparate from the Vcom electrodes.

Although FIGS. 2C-2F illustrate driving the same guarding signal acrossthe various display and sensor electrodes, this is for ease ofexplanation. In other embodiments, the DC voltages across the displayand sensor electrodes may be unique. Thus, driving the guarding signalonto the electrodes only changes the DC voltages in the electrodes inthe same manner but does not make them equivalent voltages. For example,the guarding signal may raise each voltage on the source, gate, and Vcomelectrodes by 4 V but the resulting voltage on the electrodes may bedifferent—e.g., −1 V, 3 V, and 5V, respectively. Thus, mitigating theeffect of the parasitic capacitances is not dependent on the absolutevoltage of the various electrodes but rather that the voltage across theparasitic capacitances remains substantially unchanged.

Additionally, the guarding signal may be transferred between thedifferent electrodes using capacitive coupling. For example, Vcom andgate electrodes may be located on neighboring layers in the displaydevice. As such, the guarding signal may be driven onto only one set ofthese electrodes and rely on the capacitive coupling between theelectrodes to propagate the guarding signal on both sets of electrodes.

Further, in any of the embodiments of FIGS. 2B-2F, one of the displayand sensor electrodes that contribute to the parasitic capacitivecoupling may be driven with a substantially constant signal, while theother electrodes are driven with a guarding signal as is described inFIGS. 1B-1G. Further yet, in any of the embodiments of FIGS. 2B-2F, atleast one of the display and sensor electrodes that contribute to theparasitic capacitive coupling may be electrically floated while theother electrodes are driven with a guarding signal or is electricallyfloated as is described in FIGS. 1B-1G.

FIGS. 3A-3B are schematic block diagrams of display systems for guardingdisplay electrodes during capacitive sensing, according to an embodimentdescribed herein. Specifically, the display system 300 includes gateselect logic 305 and a plurality of source drivers 310 coupled to pixels315. For example, system 300 may be part of a display device in inputdevice 100 discussed in FIG. 1A. The gate select logic 305 (alsoreferred to as row selection logic) may select one of the gateelectrodes 325 (or rows) by activating the respective transistorswitches in pixels 315. When on, these switches enable a conductive paththrough which source drivers 310 may drive a desired voltage across thecapacitors 320. The voltage on the capacitors 320 is defined by thevoltage difference between the voltage on the source electrodes 330 (orcolumn lines) connected to source driver 310 and the reference voltage(e.g., Vcom) on the common electrodes 350. In one embodiment, thecapacitance of capacitors 320 may be based on, at least in part, theliquid crystal material used to set the color associated with pixels315. However, the embodiments described herein are not limited to anyparticular display technology and may be used, for example, with LED,OLED, CRT, plasma, EL, or other display technology.

The gate select logic 305 may raster through the individual rows of thedisplay screen until all the pixels have been updated (referred toherein as a display frame update). For example, gate select logic 305may activate a single gate electrode 325 or row. In response, the sourcedrivers 310 may drive respective voltages onto the source electrodes 330that generate a desired voltage (relative to the reference voltage)across the capacitors 320 in the activated row. The gate select logic305 may then de-activate this row before activating a subsequent row. Inthis manner, the gate select logic 305 and the source drivers 310 may becontrolled by, for example, a display driver module on the processingsystem such that source drivers 310 provide the correct voltage for thepixels 315 as the gate select logic 305 activates each row.

When performing capacitive sensing, or more specifically, whenperforming absolute capacitance sensing, the gate, source, and commonelectrodes 325, 330, 350 may transmit the guarding signal. System 300includes multiplexers 340 (i.e., muxes) that may be used to transmit theguarding signal on the display electrodes. For example, when performingcapacitive sensing, the display device may switch the select signalcontrolling the muxes 340 such that the guarding signal is transmittedon the display electrodes—i.e., gate, source, and common (or cathode)electrodes 325, 330, 350. Although circuit 300 illustrates transmittingthe guarding signal on all the display electrodes, in other embodiments,only one or more of the electrodes may be selected to carry the guardingsignals while the other display electrodes are optionally electricallyfloated. For example, if the coupling capacitance between the sensorelectrodes and the source electrodes 330 is much greater than thecoupling capacitance between the sensor electrodes and the gateelectrodes 325, the guarding signal may be driven only on the sourceelectrodes 330 and the gate electrodes may be driven or electricallyfloated.

FIG. 3B illustrates using a display system 390 that uses a chargesharing system to drive the guarding signal onto the source electrodes330 and common electrodes 350. When performing capacitive sensing, thedisplay system 390 may use logic—e.g., control logic 345 and switchingelements 335—already included within the display system 390 such as acharge share system. To use this logic during capacitive sensing, thecontrol logic 345 may disable the source driver and activate switchingelements 335 such that the common electrodes 350 are connected to thesource electrodes 330. In addition, the control logic 345 instructs theswitch 340 (shown here as a mux) to drive the guarding signal 215 ontothe common electrodes 350. That is, instead of coupling the commonelectrodes 350 to the reference voltage Vcom, the common electrodes 350instead transmit the guarding signal. Because the common electrodes 350and source electrodes 330 are connected via the switching elements 335,the guarding signal is also driven onto the source lines 330. In thismanner, when performing capacitive sensing, the switches 335 in displaysystem 390 enable the transmission of the guarding signal onto sourceand common electrodes 330, 350 in order to remove the parasiticcapacitance between these electrodes and the sensor electrode (notshown).

Although FIG. 3B illustrates using switch 340 to switch between thereference voltage and the guarding signal, this is for illustrativepurpose only. In other embodiments, the common electrodes 350 may becoupled to a driver which is capable of driving either the referencevoltage or the guarding signal onto the common electrodes 350. Thus,additional hardware may not need to be added to the display system 390in order to transmit the guarding signals onto the reference and sourceelectrodes 330. Moreover, FIG. 3B illustrates only one example oftransmitting the guarding signal onto the source and common electrodes330, 350 where the display system 390 includes, for example, a chargesharing system. In another embodiment, even if the display system lacksa charge sharing system, the source driver 310 may be used to drive theguarding signal onto each of the source electrodes 330 while a separatedriver (not shown) transmits the guarding signal onto the commonelectrodes 350. That is, even if the source electrodes 330 are notcoupled to each other or are not coupled to the common electrodes 350, adisplay system may be configured to transmit the guarding signal ontothe display electrodes.

For example, when the common electrodes 350 are driven with the guardingsignal, the gate electrodes 325 and/or the source electrodes 330 may beelectrically floated to effectively remove their capacitance from thesensor electrodes. In another example, common electrodes 350 and gateelectrodes 325 may be driven with the guarding signal while the sourceelectrodes 330 may be electrically floated. In other examples, commonelectrodes 350 and source electrodes 330 may be driven with the guardingsignal while the gate electrodes 325 may be electrically floated. In yetanother example, the gate electrodes 325 may be driven with the guardingsignal while the source electrodes 330 and/or common electrodes 350 areelectrically floated. In another example, the gate electrodes 325 andsource electrodes 330 may be driven with the guarding signal while thecommon electrodes 350 may be electrically floated. In yet a furtherexample, the source electrodes 330 may be driven with a modulated signalwhile the gate electrodes 325 and/or common electrodes 350 may beelectrically floated. In the above examples, the electrically floatedelectrode(s) are modulated with the guarding signal via the couplingcapacitance between the floated electrode(s) and the drivenelectrode(s). In other examples, when one of the electrodes (commonelectrodes 350, gate electrodes 325 and source electrodes 330) is drivenwith the guard signal at least one other electrode is driven with asubstantially constant voltage.

In one embodiment, one or more of the sensor electrodes are disposedbetween a color filter glass used by the display systems shown in FIGS.3A and 3B and an input surface of the input device. In one embodiment, aset of sensor electrodes are disposed between the color filter glass ofthe display device and an input surface of the input device. Theelectrodes within the display device may comprise one or more displayelectrodes of the display device—i.e., the electrodes are used both whenupdating the display and when performing capacitive sensing. In yetanother embodiment one or more of the sensor electrodes are disposedbetween the active layer of the display device and the color filterglass, where the sensor electrodes may also be used as displayelectrodes of the display device. In a gate-in-panel system, the inputdevice may be able to switch the gate electrodes into a high-impedancestate during capacitive sensing.

FIGS. 4A-4B illustrate an integrated touch and display controller 400for guarding gate electrodes in the display system, according to anembodiment described herein. Specifically, the controller 400 may becoupled to the display system 300 in FIG. 3A to drive the guardingsignal onto the gate electrodes 325 coupled to the gate select logic305. In one embodiment, controller 400 may be the processing system 110shown in FIG. 1A. Furthermore, controller 400 may include the logicnecessary to perform both capacitive sensing and display updating in aninput device. For example, controller 400 may be a single IC chip.Although not shown, controller 400 may include the control logic 345shown in FIG. 3A which issues the control signals for driving theguarding signal onto the source and common electrodes as discussedabove.

The integrated controller 400 includes a power supply 405 and powerconverter 410. The power supply 405, which may also be external tocontroller 400, provides a power signal to the power converter 410 forgenerating a voltage for the gate electrodes 325 shown in FIG. 3A. Here,the power converter 410 generates a high gate voltage V_(GH) and a lowgate voltage V_(GL) which the gate select logic 305 in FIG. 3A may thenuse to either activate or deactivate a row of pixels 315. In oneembodiment, the integrated controller 400 may include the source drivers310. Accordingly, the integrated controller 400 may provide the sourcevoltage (V_(S)) as well as the gate voltages V_(GH) and V_(GL) to adisplay screen. In one embodiment, the guarding signal may be generated,either directly or indirectly, by modulating the power supply voltagestransmitted to the circuits that drive the display electrodes.

FIG. 4B illustrates a more detailed circuit model of the controller 400.Specifically, the charge pumps 420 generate the gate voltages V_(GH) andV_(GL). For example, the power supply 405 provides power to the chargepumps 420 which generate the gate voltages V_(GH) and V_(GL). In oneembodiment, V_(GH) may be approximately 15V while V_(GL) is −10V. Toinsert the guarding signal 215 onto the gate voltages, the powerconverter 410 includes a node coupled between reservoir capacitors C₁and C₂. These capacitors couple the guarding signal 215 into the DC gatesupply voltages generated by the power converter 410. In one embodiment,the node may be coupled to the common electrodes. Accordingly, in thismanner, the guarding signal 215 may be driven onto the gate voltagesV_(GH) and V_(GL). When the guarding signal 215 is not transmitted, thenode between the capacitors C₁ and C₂ may instead be connected to a DCvoltage. In one embodiment, the circuitry (e.g., level shifters 415) maybe designed to ensure the individual components can tolerate the voltageswings introduced by the guarding signal 215. Moreover, the levelshifters 415, which may be used to level shift the clocks and controlsignal from the display driver module to the gate select logic 305, iscoupled to the power supplies to ensure that the control signals aremodulated in a same manner as the power signals (V_(GH) and V_(GL)).Doing so automatically guards the control signals as well.

As shown by FIGS. 3A-3B and 4A-4B, the display electrodes (i.e., source,gate, and common electrodes) may drive the guarding signal 215 therebyremoving the parasitic capacitance between these electrodes and thesensor electrode. Moreover, appropriately driving the guarding signal onthe display electrodes does not affect the voltage stored in the pixelcapacitors 320, and thus, does not alter the image currently beingdisplayed on the integrated display screen. Stated differently, becausethe guarding signal changes the voltage on the display electrodes in thesame manner—i.e., the voltage swing on the display electrodes is thesame—the pixel transistors remain off which prevents the voltage on thepixel from being corrupted. Accordingly, the voltage potential acrossthe capacitors 320 remains the same thereby maintaining the displayedimage. In one example embodiment, the gate-off voltage V_(GL) may swingfrom −10V to −6V while Vcom/source lines swing from 0V to 4V based on a4V peak-to-peak guarding signal.

If the guarding signal is applied selectively to the displayelectrodes—e.g., only to the common electrodes—the guarding signal maybe designed such that the signal does not corrupt the image displayed bythe pixels. For example, if the common electrodes are driven too farnegative with respect to the voltage on the gate electrodes, theswitches may activate and cause charge to be lost from the pixels.Losing charge on the pixels may also be prevented by driving theguarding signal only in the positive direction or by reducing thegate-off voltage to prevent activation of the transistor.

FIG. 5 is a schematic block diagram of a display system 500 wheredisplay electrodes are used for performing capacitive sensing, accordingto an embodiment described herein. Specifically, display system 500illustrates that the electrodes used when updating the display may alsobe used as sensor electrodes when performing capacitive sensing. In oneembodiment, the common electrodes 350 coupled to the capacitors 320 maybe used as one or more of the sensor electrodes 120 shown in FIG. 1A.That is, instead of disposing the sensor electrodes above the displayscreen, the common electrodes 350 may serve as one or more of the sensorelectrodes. To selectively drive a modulated signal on the commonelectrodes 350, display system 500 includes a plurality of transmitters505 coupled to a respective common electrode 350. Using the switchingelements 510, each common electrode 350 may be electrically isolatedfrom the other electrodes 350 which permits a signal generator 505 todrive a unique signal on the common electrode 350 while the othertransmitters 505 may drive a different signal on the other electrodes.

For example, if the common electrodes 350 are currently being used asthe sensor electrodes for absolute capacitive sensing, the transmitters505 may transmit the modulated signal onto the common electrodes 350. Todrive the guarding signal onto the source electrodes 330, display system500 may still use switches 335 to electrically connect the sourceelectrodes 330 to the guarding signal outputted from the mux. Usingswitching elements 510, the guarding signal may be selectively drivenonto common electrodes 350. For example, the guarding signal may bedriven on all the common electrodes 350 that are currently not beingsensed (i.e., all the electrodes 350 that are not being driven using thetransmitter signal). When not performing capacitive sensing, the sourceelectrodes 330 may be disconnected from the common electrodes 350 usingswitches 335 and the mux may output Vcom on the electrodes 350 usingswitches 510.

While not illustrated in FIGS. 3A-B and 5, a switching mechanism may becoupled to one or more display electrodes to tri-state or electricallyfloat the display electrodes. This may be coupled to each of the displayelectrodes or only to subsets of the display electrodes. For example,one or more of the common electrodes, source electrodes and gateelectrodes may be coupled to a switching mechanism to electrically floatthose electrodes.

To form the capacitive profiles or capacitive image, the input devicemay sequentially drive on all of the common electrodes 350 or rasterthrough each common electrode 350 using the respective transmitter 505to measure a capacitance value associated with the electrodes 350. Inone embodiment, the input device may then sequentially drive through theset of sensor electrodes that are external to the display screen. Assuch, the guarding signal may be driven on the common electrodes 350while the modulated signal is driven on the external sensor electrodes.

CONCLUSION

Driving a guarding signal on display electrodes as well as the sensorelectrodes currently not being used to make a capacitive measurement maymitigate the effect of the coupling capacitance when measuringcapacitance associated with a sensor electrode, reduce powerconsumption, or improving settling time. In one embodiment, the displayelectrode may have similar characteristics as the modulated signal(e.g., similar amplitude and/or phase). By driving a guarding signalthat is substantially similar to the modulated signal onto the displayelectrodes, the voltage difference between the sensor electrode anddisplay electrodes remains the same. Accordingly, the couplingcapacitance between the sensor electrode and the display electrodes doesnot affect the capacitance measurement.

Thus, the embodiments and examples set forth herein were presented inorder to best explain the embodiments in accordance with the presenttechnology and its particular application and to thereby enable thoseskilled in the art to make and use the invention. However, those skilledin the art will recognize that the foregoing description and exampleshave been presented for the purposes of illustration and example only.The description as set forth is not intended to be exhaustive or tolimit the invention to the precise form disclosed.

In view of the foregoing, the scope of the present disclosure isdetermined by the claims that follow.

I claim:
 1. An input device comprising: a plurality of sensor electrodeseach comprising at least one of a plurality of common electrodes of adisplay, wherein the plurality of common electrodes are configured fordisplay updating and capacitive sensing; a plurality of displayelectrodes; and a processing system coupled to the plurality of sensorelectrodes and the plurality of display electrodes, the processingsystem is configured to: drive a modulated signal onto a first sensorelectrode of the plurality of sensor electrodes to acquire a change ofcapacitance during a first period, and operate a first display electrodeof the plurality of display electrodes in a guard mode to mitigate aneffect of a coupling capacitance between the first sensor electrode andthe first display electrode during the first period, wherein mitigatingthe effect of the coupling capacitance comprises maintaining a constantvoltage difference between the first sensor electrode and the firstdisplay electrode during the first period.
 2. The input device of claim1, wherein the processing system is configured to, when operating thefirst display electrode in the guard mode, drive the first displayelectrode with a guarding signal.
 3. The input device of claim 2,wherein the guarding signal and the modulated signal are similar in atleast one of phase, amplitude and frequency.
 4. The input device ofclaim 1, wherein the processing system is configured to, when operatingthe first display electrode in the guard mode, electrically float thefirst display electrode.
 5. The input device of claim 1, wherein thefirst display electrode is a source electrode.
 6. The input device ofclaim 1, wherein the first display electrode is a gate electrode.
 7. Theinput device of claim 1, wherein the processing system is furtherconfigured to operate a second display electrode of the plurality ofdisplay electrodes in the guard mode during the first period.
 8. Theinput device of claim 7, wherein the processing system is configured to,when operating the first display electrode in the guard mode, drive thefirst display electrode with a guarding signal and electrically floatthe second display electrode.
 9. The input device of claim 8, whereinthe first display electrode is a source electrode and the second displayelectrode is a gate electrode.
 10. The input device of claim 1, whereinthe processing system is configured to drive a second one of theplurality of sensor electrodes with a guarding signal during the firstperiod.
 11. The input device of claim 1, wherein the plurality of sensorelectrodes are disposed in a common layer.
 12. The input device of claim1, wherein the processing system comprises a first controller configuredto drive the modulated signal onto the first sensor electrode and asecond controller configured operate the first display electrode in theguard mode.
 13. The input device of claim 12, wherein the firstcontroller is synchronized with the second controller.
 14. The inputdevice of claim 1, wherein the processing system comprises a controllerconfigured to drive the modulated signal onto the first sensor electrodeand configured to operate the first display electrode in the guard mode.15. A processing system for an input device comprising: a sensor modulecomprising sensor circuitry, wherein the sensor module is configured tobe coupled to a plurality of sensor electrodes and is configured todrive, during a first time period, a first sensor electrode of theplurality of sensor electrodes with a modulated signal for capacitivesensing, wherein each sensor electrode of the plurality of sensorelectrodes comprise at least one of a plurality of common electrodes,wherein the plurality of common electrodes is configured for updating adisplay of a display device and for capacitive sensing, wherein thefirst sensor electrode of the plurality of sensor electrodes iscapacitively coupled with a first display electrode of a plurality ofdisplay electrodes and wherein the first display electrode is configuredto be operated in a guard mode during the first time period such thatthat a voltage difference between the first sensor electrode and thefirst display electrode remains constant during the first time period.16. The processing system of claim 15, wherein the sensor module, whenoperating the first display electrode in the guard mode, is configuredto drive the first display electrode with a guarding signal.
 17. Theprocessing system of claim 16, wherein the sensor module, when operatingthe first display electrode in the guard mode, is configured toelectrically float the first display electrode.
 18. A processing systemfor a display device, the processing system comprising: a display drivermodule comprising display driver circuitry configured for coupling to aplurality of display electrodes, the display driver module configuredto: drive a first display electrode of the plurality of displayelectrodes for display updating, wherein the first display electrode iscapacitively coupled to a first sensor electrode, and operate the firstdisplay electrode in a guard mode during a first period such that avoltage difference between the first display electrode and the firstsensor electrode remains constant during the first period.
 19. Theprocessing system of claim 18, wherein the processing system furthercomprises: a sensor module coupled to a plurality of sensor electrodes,the sensor module configured to drive the first sensor electrode with amodulated signal for capacitive sensing.
 20. The processing system ofclaim 19, wherein the display driver module, when operating the firstdisplay electrode in the guard mode, is further configured to drive thefirst display electrode with a guarding signal, wherein the modulatedsignal and the guarding signal have at least one of a similar phase,amplitude and frequency.